Mimo Symbol Detection for Snr Higher and Lower Than a Threshold

1. A system for detecting a plurality of symbols communicated from multiple transmitting antennas to multiple receiving antennas, comprising: a first detector that determines the symbols from a plurality of respective partial distances of a first plurality of potential choices for at least one of the symbols from a constellation, the first detector determining the respective partial distances from a plurality of signals received at the receiving antennas; wherein the first detector comprises a K-best sphere detector; a second detector that determines the symbols from a plurality of respective partial distances of a second plurality of potential choices for at least one of the symbols from the constellation, the second detector determining the respective partial distances from the signals, and in response to a signal-to-noise ratio (SNR) of the signals being higher than a threshold the second plurality is fewer in number than the first plurality; wherein the second detector comprises a depth-first-search maximum-likelihood detector that prunes each second potential choice having the respective partial distance that is not less than the respective partial distance of one of the second potential choices; wherein the one of the second potential choices includes respective symbols for all of the symbols communicated from the transmitting antennas to the receiving antennas; wherein the respective partial distance of the one of the second potential choices is a distance between the respective symbols and the signals received at the receiving antennas; and an evaluator coupled to the first and second detectors, the evaluator estimating the SNR of the signals received at the receiving antennas, wherein the evaluator enables the first detector to determine the symbols in response to the SNR being lower than the threshold, and the evaluator enables the second detector to determine the symbols in response to the SNR being higher than the threshold.

2. The system of claim 1 , wherein the second plurality is larger than the first plurality in response to the SNR being lower than the threshold.

3. The system of claim 1 , wherein: the second plurality varies with the SNR of the signals, with the second plurality being smaller than the first plurality in response to the SNR being higher than the threshold and the second plurality being larger than the first plurality in response to the SNR being lower than the threshold; and the evaluator enables the first and second detectors to determine the respective partial distances for only a smaller of the first and second pluralities at the SNR of the signals, while achieving approximately the bit error rate of the second detector.

4. The system of claim 1 , wherein: the evaluator puts the second detector into a disabled low-power mode in response to the SNR being lower than the threshold; and the evaluator puts the first detector into a disabled low-power mode in response to the SNR being higher than the threshold.

5. The system of claim 1 , wherein the first and second detectors are implemented in an array of programmable logic and routing resources of a programmable integrated circuit.

6. The system of claim 5 , further comprising a dynamic reconfiguration block adapted to implement the first detector in the array and not to implement the second detector in the array while the SNR is lower than the threshold, and adapted to implement the second detector in the array and not to implement the first detector in the array while the SNR is higher than the threshold.

7. The system of claim 6 , wherein the programmable logic and interconnect resources for implementing the first detector overlap the programmable logic and interconnect resources for implementing the second detector.

8. The system of claim 1 , wherein the system comprises the first and second detectors in a time multiplexed manner, the system including the first detector and not the second detector during at least a first time period, and the system including the second detector and not the first detector during at least a second time period.

9. The system of claim 1 , wherein: the first detector includes a plurality of respective stages associated with the transmitting antennas and coupled in a sequence; each respective stage other than a final stage in the sequence selects a plurality of candidates and the final stage selects a final candidate in response to the received signals; each candidate of each respective stage includes a symbol for the respective stage and a symbol for each of the stages that precedes the respective stage in the sequence; and the final candidate includes the symbols detected as communicated from the transmitting antennas to the receiving antennas.

10. The system of claim 9 , wherein: each respective stage other than the final stage includes a distance block and a selector; the final stage includes a distance block and an identifier block; the distance block of an initial stage in the sequence determining the respective partial distances of the first potential choices pairing a null candidate with each of a plurality of symbols in the constellation; the distance block of each respective stage other than the initial stage determines the respective partial distances of the first potential choices pairing each of the candidates of a preceding stage in the sequence and each of the symbols in the constellation: the selector of each respective stage other than the final stage selects the candidates from the potential choices of the distance block of the respective stage; the selector selects the candidates as the potential choices having smaller ones of the respective partial distances; the identifier of the final stage selects the final candidate from the potential choices of the distance block of the final stage; and the identifier selects the final candidate as one of the potential choices having a smaller one of the respective partial distances.

11. The system of claim 10 , wherein: the selector of each respective stage other than the final stage selects the candidates as a predetermined number of the potential choices of the respective stage having smallest ones of the respective partial distances; and the identifier selects the final candidate as one of the potential choices of the identifier having a smallest one of the respective partial distances.

12. The system of claim 11 , wherein the predetermined number of the potential choices for each respective stage other than the final stage is a same number for every one of the respective stages except the final stage.

13. An article of manufacture, comprising: a processor-readable device configured with instructions for generating configuration data for a programmable integrated circuit, wherein execution of the instructions by a processor causes the processor to generate the configuration data, and configuring the programmable integrated circuit with the configuration data causes the programmable integrated circuit to implement: a first detector that determines the symbols from a plurality of respective partial distances of a first plurality of potential choices for at least one of the symbols from a constellation, the first detector determining the respective partial distances from a plurality of signals received at the receiving antennas, the first detector enabled to determine the symbols in response to a signal-to-noise ratio (SNR) of the signals being lower than a threshold; wherein the first detector comprises a K-best sphere detector; a second detector that determines the symbols from a plurality of respective partial distances of a second plurality of potential choices for at least one of the symbols, the second detector determining the respective partial distances from the signals, the second detector enabled to determine the symbols in response to the SNR being higher than the threshold, and the second plurality is smaller than the first plurality in response to the SNR being higher than the threshold; wherein the second detector comprises a depth-first-search maximum-likelihood detector that prunes each second potential choice having the respective partial distance that is not less than the respective partial distance of one of the second potential choices; wherein the one of the second potential choices includes respective symbols for all of the symbols communicated from the transmitting antennas to the receiving antennas; and wherein the respective partial distance of the one of the second potential choices is a distance between the respective symbols and the signals received at the receiving antennas.

14. The article of manufacture of claim 13 , wherein the configuring of the programmable integrated circuit with the configuration data further causes the programmable integrated circuit to implement a dynamic reconfiguration block adapted to implement the first detector in the programmable integrated circuit and not to implement the second detector in the programmable integrated circuit while the SNR is lower than the threshold, and further adapted to implement the second detector in the programmable integrated circuit and not to implement the first detector in the programmable integrated circuit while the SNR is higher than the threshold.

15. The article of manufacture of claim 14 , wherein: the first and second detectors are each implemented in the programmable integrated circuit within an array of programmable logic and interconnect resources of the programmable integrated circuit; and the programmable logic and interconnect resources for implementing the first detector overlap the programmable logic and interconnect resources for implementing the second detector.

16. The article of manufacture of claim 13 , wherein: the second plurality varies with the SNR of the signals, with the second plurality being smaller than the first plurality in response to the SNR being higher than the threshold and the second plurality being larger than the first plurality in response to the SNR being lower than the threshold; and the first and second detectors are enabled to determine the respective partial distances for only a smaller of the first and second pluralities at the SNR of the signals, while achieving approximately the bit error rate of the second detector.

17. A system for detecting a plurality of symbols from a constellation that are communicated from multiple transmitting antennas to multiple receiving antennas, comprising: means for evaluating a signal-to-noise ratio (SNR) of signals received at the receiving antennas; first means for detecting the symbols from the signals in response to the SNR being lower than a threshold; and second means for detecting the symbols from the signals in response to the SNR being higher than the threshold, wherein: a bit error rate of the second means is less than a bit error rate of the first means, and the second means performs fewer calculations than would the first means in response to the SNR being higher than the threshold and the first means performs fewer calculations than would the second means in response to the SNR being lower than the threshold.

18. The system of claim 17 , further comprising means for reconfiguring a programmable integrated circuit to implement the first means during a first time period and the second means during a second time period.